Use timestamping with openbts or a similar BTS software

[LuLu-1001]

I am genuinely curious if it is possible to adapt this to work with a 2G bts software. I am trying to do a project that requires a 2g bts however I only have a plutosdr. Would this be possible and how easy would it be?

[pgreenland]

Hey,

Apologies for the crazy slow reply. I thought Github would notify me of a new issue being raised but I may not having things set quite right.

A 2G version of this setup has been on my plans for a while....as has a 5G version (providing the Pluto is capable) now srsRAN have their 5G stack out.

In terms of timestamping thats been implemented generically. If you can find a 2G stack that uses SoapySDR, it stands of chance of working.

I've not explored myself too much yet, but if you've found a stack you'd like to try it with let me know.

Regards,

Phil

[VasylSamoilov]

Only working 2G stack that is practical is osmocom, and component responsible for sdr operations is osmo-trx. Right now it only supports limesdr and usrp uhd drivers - see https://github.com/osmocom/osmo-trx/tree/master/Transceiver52M/device .
The problem here is (possibly) that osmo-trx operates the base station clock based upon the sample count of received samples, adapting transceiver the stay ahead bases on latency and underruns. Probably it can be adapted to this SoapySDR/libiio implementation, but hardly anybody can pull it off except @pgreenland :)

[pgreenland]

Thanks for the pointers. Those RF interfaces look very similar to the ones in srsRAN. The BladeRF support appears to have some comments regarding buffer size limitations of the device and the delays / gaps that will occasionally occur in the RF samples.

Providing the number of RF samples required each timeslot is fixed, which a bit of googling suggests that it is for GSM, it should drop in quite nicely.

The challenge as always will be finding time to do it I suspect :-(

[VasylSamoilov]

Given that GSM channel bandwidth is 200kHz maybe osmo-trx for pluto can run on device itself, connecting to osmo-bts via network, making it a perfect gsm base station trx for osmocom :) trx udp protocol is much more efficient than sending IQ samples over network. Probably such use case is what pluto designers had in mind.

BTW osmocom runs on raspberry pi without a problem and have appropriate builds for ARM architecture.

I completely understand - finding the time for projects like this can be challenging. If there's any way I can help - please don't hesitate to let me know. Mostly I can build and test, I presume :)

[LunaWuna]

I know it's not a high priority or the original goal of the project but I also have an interest in getting openbts/osmotrx to work as my country hasn't had an active GSM network since 2017.